Description

Composition

Tungstates of iron and manganese, the two elements form a continuous series with end members known as ferberite (with *3.7% FeO and *6.3% WO 3) and huebnerite (with *3.4% MnO and *6.6% WO 3).

Tests

Decrepitates (flies apart), then fuses to a globule that assumes, on solidifying, a slightly faceted (crystalline) surface (that from ferberite is magnetic). The best tungsten test is to fuse the material on the charcoal under sodium carbonate, dissolve the slaggy mixture in strong hydrochloric acid, and add pure tin, which imparts a blue color to the solution. It's best to try out this test several times with known tungsten-bearing ores, to acquire the technique. Exaggerated heat sensitivity makes crystals vulnerable to damage if too intensely illuminated, as in the mineral-show display cases.

Distinguishing characteristics

The tungsten test is the best guide and may be essential. Manganese-rich huebnerite can resemble goethite, which is magnetic (huebnerite is not magnetic after fusion) and will give no tungsten test. It also resembles columbite, tantalite, and manganotantalite, and again the tungsten test is the one to apply, although tungsten sometimes can be found in these minerals; then the problem may become complicated.